There are generally four (4) main types of automotive power train (“driveline systems”). More specifically, there exists a full-time front wheel drive system, a full-time rear wheel drive system, a part-time four wheel drive system, and an all-wheel drive system. Most commonly, the systems are distinguished by the delivery of power to different combinations of drive wheels, i.e., front drive wheels, rear drive wheels or some combination thereof. In addition to delivering power to a particular combination of drive wheels, most drive systems permit the respectively driven wheels to rotate at different speeds. For example, the outside wheels must rotate faster than the inside drive wheels, and the front drive wheels must normally rotate faster than the rear wheels.
Driveline systems also include one or more constant velocity joints (CVJ's). Such joints, which include by way of example, and not limitation, the plunging tripod type and the high speed fixed type, are well known to those skilled in the art and are employed where transmission of a constant velocity rotary motion is desired or required. A typical driveline system for a rear wheel or all wheel drive vehicle, for example, incorporates one or more constant velocity joints to connect a pair of front and rear propeller shafts (“propshafts”) to transfer torque from a power take off unit to a rear drive line module. Similarly, a drive line system for a front wheel drive vehicle incorporates one or more constant velocity joints to transfer torque from a power take off unit to a rotary drive shaft.
As those skilled in the art are aware, at certain rotational speeds and resonant frequencies, the above referenced propshafts and driveshafts (hereinafter collectively referred to as driveshafts), are known to exhibit unbalanced rotation and thus undesirable vibrations. These vibrations, in turn, are known to result in bending or torsional forces within and along the length of the respective driveshaft. It is obvious that such bending or torsional forces due to unbalanced rotation are neither desirable nor suitable in the operation of the drive train of most vehicles.
Dynamic dampers and mass dampers have heretofore been used to suppress undesirable vibrations that are induced in rotary driveshafts due to unbalanced rotation. Such dampers are often installed or inserted directly onto the rotary driveshafts. See, for example, U.S. Pat. No. 5,056,763 to Hamada, et al. As disclosed, the dynamic damper of Hamada, et al. comprises a pair of ring shaped fixing members spaced apart at predetermined intervals with a mass member disposed therebetween. A pair of connecting members are then provided to connect the ends of the fixing members to the ends of the mass member. In operation, the Hamada et al. damper transfers and absorbs the vibrational energy of the rotary drive shaft by generating a prescribed vibrational frequency adjusted to the dominant frequency of the vibrations. The dynamic damper thus cancels or negates vibrations that are induced onto or caused by the rotary driveshaft in normal operation of the drive train of the vehicle. As readily seen, however, the Hamada et al damper does not address, let alone increase, the threshold resonant frequency at which harmful bending of the driveshaft will occur in the first place.
As those skilled in the art will recognize, shorter length driveshafts have corresponding higher resonant frequencies of bending. Thus, current practice for increasing such resonant frequencies requires the use of multi-part (typically 3 pieces) drive shaft assemblies with respective shorter lengths. Such multi-piece assemblies, however, require greater expense to manufacture and greater labor and skill to install.
Consequently, a need exists for a rotary driveshaft which functions to not only negate undesirable vibrations caused by unbalanced rotation, but to increase the resonant frequency of bending of the driveshaft itself. There also is the need in the art for a driveshaft having fewer components and sections.